E05-012: Measurement of polarization observables in eta-photoproduction with CLAS

E06-013: Measurement of p+p- Photoproduction in Double-Polarization Experiments using CLAS.

These experiments have a common physics goal: "baryon spectroscopy," the study of the excitation of protons and neutrons (baryons). In the experiment, high-energy photons will collide with target protons. A proton can absorb part of the photon's energy and may get excited into what is called a baryon resonance.

Some resonances have already been observed, and their properties are known reasonably well. For others, there are only vague experimental indications. Finally, some are predicted by theory, but have never been seen in experiments. The goal of G9-Frost is to better measure the properties of known baryon resonances, to confirm the existence of those that are poorly known, and to also look for those that might be missing.

Resonances are very short-living particles. Once produced, they almost immediately break apart, or decay, into a few other particles. The particles will be detected in Hall B's CEBAF Large Acceptance Spectrometer, which will measure their directions and energies. With this information, scientists are trying to understand the mechanism of production and decay and also the properties of the resonances.

The incoming photons' spin will be aligned in one direction (polarized). The target protons will also be polarized in the Frozen Spin Target (FROST), which was built to align and hold the spins of the protons. FROST is the first target of its kind at JLab and this experiment is the first of its kind to use a polarized photon beam with a polarized target.

This is the next step toward a "complete experiment" - one in which enough information is obtained to reconstruct a process in question almost independent of any models.